In humans and other vertebrate animals, the heart is a hollow muscular organ having four pumping chambers separated by four heart valves: aortic, mitral (or bicuspid), tricuspid, and pulmonary. The valves open and close in response to a pressure gradient during each cardiac cycle of relaxation and contraction to control the flow of blood to a particular region of the heart and/or to blood vessels (pulmonary, aorta, etc.)
These valves are comprised of a dense fibrous ring known as the annulus, and leaflets or cusps attached to the annulus. For some valves, there is also a complex of chordae tendinae and papillary muscles securing the leaflets. The size of the leaflets or cusps is such that when the heart contracts the resulting increased blood pressure formed within heart chamber forces the leaflets open to allow flow from the heart chamber. As the pressure in the heart chamber subsides, the pressure in the subsequent chamber or blood vessel becomes dominant, and presses back against the leaflets. As a result, the leaflets or cusps come in apposition to each other, thereby closing the passage.
Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood through the valve when the valve is closed. Valve disease can be severely debilitating and even fatal if left untreated. Various surgical techniques may be used to replace or repair a diseased or damaged valve. In a traditional valve replacement operation, the damaged leaflets are typically excised and the annulus sculpted to receive a replacement prosthetic valve.
In many patients who suffer from dysfunction of the mitral and/or tricuspid valves(s) of the heart, surgical repair of the valve (i.e., “valvuloplasty”) is a desirable alternative to valve replacement. For some patients, however, the condition of the native heart valve requires complete replacement using a prosthetic heart valve. Prosthetic heart valves have been known for some time, and have been successfully implanted using traditional open-chest surgical approaches, minimally-invasive procedures, and so-called percutaneous methods.
A prosthetic heart valve typically comprises a support structure (such as a ring and/or stent) with a valve assembly deployed therein. The support structure is often rigid, and can be formed of various biocompatible materials, including metals, plastics, ceramics, etc. Two primary types of “conventional” heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a ball and cage arrangement or a pivoting mechanical closure supported by a base structure to provide unidirectional blood flow, such as shown in U.S. Pat. No. 6,143,025 to Stobie, et al. and U.S. Pat. No. 6,719,790 to Brendzel, et al., the entire disclosures of which are hereby expressly incorporated by reference. The other is a tissue-type or “bioprosthetic” valve having flexible leaflets supported by a base structure and projecting into the flow stream that function much like those of a natural human heart valve and imitate their natural flexing action to coapt against each other and ensure one-way blood flow.
In tissue-type valves, a whole xenograft valve (e.g., porcine) or a plurality of xenograft leaflets (e.g., bovine pericardium) can provide fluid occluding surfaces. Synthetic leaflets have been proposed, and thus the term “flexible leaflet valve” refers to both natural and artificial “tissue-type” valves. In a typical tissue-type valve, two or more flexible leaflets are mounted within a peripheral support structure that usually includes posts or commissures extending in the outflow direction to mimic natural fibrous commissures in the native annulus. Components of the valve are usually assembled with one or more biocompatible fabric (e.g., Dacron) coverings, and a fabric-covered sewing ring is provided on the inflow end of the peripheral support structure.
In many bioprosthetic-type valves, a metallic or polymeric structure provides base support for the flexible leaflets, which extend therefrom. One such support is a “support frame,” sometimes called a “wireform” or “stent,” which has a plurality (typically three) of large radius cusps supporting the cusp region of the flexible leaflets (i.e., either a whole xenograft valve or three separate leaflets). The ends of each pair of adjacent cusps converge somewhat asymptotically to form upstanding commissures that terminate in tips, each extending in the opposite direction as the arcuate cusps and having a relatively smaller radius. The support frame typically describes a conical tube with the commissure tips at the small diameter end. This provides an undulating reference shape to which a fixed edge of each leaflet attaches (via components such as fabric and sutures) much like the natural fibrous skeleton in the aortic annulus. One example of the construction of a flexible leaflet valve is seen in U.S. Pat. No. 6,585,766 to Huynh, et al. (issued Jul. 1, 2003), in which the exploded view of FIG. 1 illustrates a fabric-covered wireform 54 and a fabric-covered support stent 56 on either side of a leaflet subassembly 52. The contents of U.S. Pat. No. 6,585,766 are hereby incorporated by reference in their entirety. Other examples of valve and related assemblies/systems are found in U.S. Pat. No. 7,137,184, which issued on Nov. 21, 2006, the contents of which are hereby incorporated by reference in their entirety.
Sometimes the need for complete valve replacement may arise after a patient has already had an earlier valve replacement for the same valve. For example, a prosthetic heart that was successfully implanted to replace a native valve may itself suffer damage and/or wear and tear many years after initially being implanted.
Implanting a prosthetic heart valve into a patient with a previously-implanted prosthetic heart valve typically involves additional steps from a similar procedure in a patient with no previously-implanted heart valve. Implanting the prosthetic heart valve directly within a previously-implanted prosthetic heart valve is generally impractical, in part because the new prosthetic heart valve (including the support structure and valve assembly) will have to reside within the annulus of the previously-implanted heart valve, and traditional prosthetic heart valves are not configured to easily receive such a valve-within-a-valve implantation in a manner which provides secure seating for the new valve while also having a large enough annulus within the new valve to support proper blood flow therethrough. Implanting a prosthetic heart valve in a patient who previously had a prosthetic heart valve generally requires the previously-implanted heart valve to be removed during the same procedure in which the new prosthetic heart valve is implanted. In such cases, a surgeon can use a traditional surgical approach to install the prosthetic valve, which can involve the surgeon cutting out the previously-implanted heart valve from the heart valve annulus, and then implanting the new prosthetic valve into the heart valve annulus.
Percutaneous and minimally-invasive heart valve replacement has been developed recently, wherein a prosthetic heart valve is advanced percutaneously (e.g., via the femoral artery or other desired approaches) or via other approaches (i.e., minimally-invasive “keyhole” surgery, including approaches via the apex of the heart, etc.) into the heart valve annulus, and then expanded within the heart valve annulus. Various expandable valves are being tested, primarily that use balloon- or self-expanding stents as anchors. For the purpose of inclusivity, the entire field will be denoted herein as the delivery and implantation of expandable valves, regardless of whether the delivery method involves percutaneous, minimally-invasive, or other delivery methods. These valves typically include a scaffold or frame that expands radially outward into direct anchoring contact with the annulus, sometimes assisted with barbs. Examples of percutaneous heart valves and delivery systems and methods therefore are described in U.S. Pat. No. 5,411,552, issued May 2, 1995; U.S. Pat. No. 5,840,081, issued Nov. 24, 1998; U.S. Pat. No. 6,168,614, issued Jan. 2, 2001; and U.S. Pat. No. 6,582,462, issued Jun. 24, 2003; and also in U.S. patent application Ser. No. 11/280,062, filed Nov. 16, 2005; U.S. patent application Ser. No. 11/488,510, filed Jul. 18, 2006; and U.S. patent application Ser. No. 11/542,087, filed Oct. 2, 2006; the contents of each of which are hereby incorporated by reference in their entirety.
Percutaneous heart valve replacement is often performed without cutting out the native heart valve, wherein the prosthetic heart valve is expanded in the native heart valve annulus and the native valve leaflets are pressed against the valve annulus walls by the expanded prosthetic heart valve. However, in cases where a previously-implanted prosthetic heart valve is present, deploying a prosthetic heart valve within the native heart valve may be impractical. The shape and structure of the previously-installed prosthetic heart valve may interfere with the proper placement, deployment, and functioning of the new prosthetic heart valve.
There is thus a need for a prosthetic heart valve which will properly replace a damaged heart valve, but will also enable a replacement expandable prosthetic heart valve to be deployed therein at a later time. The current invention meets this need.